Xiaoqin Yan

Scanning Probe Study on the Piezotronic Effect in ZnO Nanomaterials and Nanodevices

ZnO nanomaterials with their unique semiconducting and piezoelectric coupled properties have become promising materials for applications in piezotronic devices including nanogenerators, piezoelectric field effect transistors, and diodes. This article will mainly introduce the research progress on piezotronic properties of ZnO nanomaterials investigated by scanning probe microscopy (SPM) and ZnO-based prototype piezotronic nanodevices built in virtue of SPM, including piezoelectric field effect transistors, piezoelectric diodes, and strain sensors. Additionally, nanodamage and nanofailure of ZnO materials and their relevant piezotronic nanodevices will be critically discussed in their safe service in future nanoelectromechanical system (NEMS) engineering.

Highly transparent triboelectric nanogenerator for harvesting water-related energy reinforced by antireflection coating

Water-related energy is an inexhaustible and renewable energy resource in our environment, which has huge amount of energy and is not largely dictated by daytime and sunlight. The transparent characteristic plays a key role in practical applications for some devices designed for harvesting water-related energy. In this paper, a highly transparent triboelectric nanogenerator (T-TENG) was designed to harvest the electrostatic energy from flowing water. The instantaneous output power density of the T-TENG is 11.56 mW/m2. Moreover, with the PTFE film acting as an antireflection coating, the maximum transmittance of the fabricated T-TENG is 87.4%, which is larger than that of individual glass substrate. The T-TENG can be integrated with silicon-based solar cell, building glass and car glass, which demonstrates its potential applications for harvesting waste water energy in our living environment and on smart home system and smart car system.

Electronic structure engineering of Cu2O film/ZnO nanorods array all-oxide p-n heterostructure for enhanced photoelectrochemical property and self-powered biosensing application.

We have engineered the electronic structure at the interface between Cu2O and ZnO nanorods (NRs) array, through adjusting the carrier concentration of Cu2O. The electrodeposition of Cu2O at pH 11 acquired the highest carrier concentration, resulting in the largest interfacial electric field between Cu2O and ZnO, which finally led to the highest separation efficiency of photogenerated charge carriers. The optimized Cu2O/ZnO NRs array p-n heterostructures exhibited enhanced PEC performance, such as elevated photocurrent and photoconversion efficiency, as well as excellent sensing performance for the sensitive detection of glutathione (GSH) in PBS buffer even at applied bias of 0 V which made the device self-powered. Besides, the favorable selectivity, high reproducibility and extremely wide detection range, make such heterostructure a promising candidate for PEC biosensing applications, probably for the extended field of PEC water splitting or other solar photovoltaic beacons.

Self-Powered UV Photosensor Based on PEDOT:PSS/ZnO Micro/Nanowire with Strain-Modulated Photoresponse

Developing tailored micro/nanostructure interfaces is an effective way to make novel optoelectronic devices or enhance their performances. Here we report the fabrication of a PEDOT:PSS/ZnO micro/nanowire-based self-powered UV photosensor. The generation of photocurrent at zero bias is attributed to the separation of photogenerated electron-hole pairs within the built-in electric field at the PEDOT:PSS/ZnO interface upon UV light illumination. Furthermore, the piezotronic effect on the UV photoresponsivity under different strains is investigated, which is due to the modification of energy band diagram at the p-n heterojunction by strain-induced piezoelectric polarization. This study demonstrates a prospective approach to engineering the performance of a photodetector through straining and may offer theoretical supporting in future optoelectronic device fabrication and modification.

Enhanced photoelectrochemical property of ZnO nanorods array synthesized on reduced graphene oxide for self-powered biosensing application

We have realized the direct synthesis of ZnO nanorods (ZnO NRs) array on reduced graphene layer (rGO), and demonstrated the enhanced photoelectrochemical (PEC) property of the rGO/ZnO based photoanode under UV irradiation compared with the pristine ZnO NRs array. The introduction of the rGO layer resulted in a favorable energy band structure for electron migration, which finally led to the efficient photoinduced charge separation. Such nanostructure was subsequently employed for self-powered PEC biosensing of glutathione in the condition of 0 V bias, with a linear range from 10 to 200 µM, a detection limit of 2.17 µM, as well as excellent selectivity, reproducibility and stability. The results indicated the rGO/ZnO nanostructure is a competitive candidate in the PEC biosensing field.

Improved glucose electrochemical biosensor by appropriate immobilization of nano-ZnO

We constructed the transferred ZnO biosensor and the grown ZnO biosensor by two different nano-ZnO immobilization approaches. And the influence of different assembly processes on the biosensor performance has been systematically investigated and compared. An enhanced sensitivity of the grown ZnO biosensor is found to be 52% higher than that of the transferred ZnO biosensor. Correspondingly, the other properties are also better in the grown ZnO biosensor, including the response time, the detection limit and the linear range. These results are well consistent with the fact that more glucose oxidase is immobilized on the well-aligned ZnO arrays, which have higher specific surface area and more direct electron communication path, in the grown sensor than the randomly distributed and stacked ZnO nanorods in the transferred sensor. The nano-ZnO grown directly has been demonstrated more desirable for enzymatic immobilization and signal transduction in the high performance biosensors.

Enhanced photoresponse of Cu2O/ZnO heterojunction with piezo-modulated interface engineering

The ability to arbitrarily regulate semiconductor interfaces provides the most effective way to modulate the performance of optoelectronic devices. However, less work has been reported on piezo-modulated interface engineering in all-oxide systems. In this paper, an enhanced photoresponse of an all-oxide Cu2O/ZnO heterojunction was obtained by taking advantage of the piezotronic effect. The illumination density-dependent piezoelectric modulation ability was also comprehensively investigated. An 18.6% enhancement of photoresponse was achieved when applying a −0.88% compressive strain. Comparative experiments confirmed that this enhancement could be interpreted in terms of the band modification induced by interfacial piezoelectric polarization. The positive piezopotential generated at the ZnO side produces an increase in space charge region in Cu2O, thus providing an extra driving force to separate the excitons more efficiently under illumination. Our research provides a promising method to boost the performance of optoelectronics without altering the interface structure and could be extended to other metal oxide devices.

Self-Powered Photoelectrochemical Biosensor Based on CdS/RGO/ZnO Nanowire Array Heterostructure.

A CdS/reduced graphene oxide (RGO)/ZnO nanowire array (NWAs) heterostructure is designed, which exhibits enhanced photoelectrochemical (PEC) activity compared to pure ZnO, RGO/ZnO, and CdS/ZnO. The enhancement can be attributed to the synergistic effect of the high electron mobility of ordered 1D ZnO NWAs, extended visible-light absorption of CdS nanocrystals, and the formed type II band alignment between them. Moreover, the incorporation of RGO further promotes the charge carrier separation and transfer process due to its excellent charge collection and shuttling characteristics. Subsequently, the CdS/RGO/ZnO heterostructure is successfully utilized for the PEC bioanalysis of glutathione at 0 V (vs Ag/AgCl). The self-powered device demonstrates satisfactory sensing performance with rapid response, a wide detection range from 0.05 mm to 1 mm, an acceptable detection limit of 10 μm, as well as certain selectivity, reproducibility, and stability. Therefore, the CdS/RGO/ZnO heterostructure has opened up a promising channel for the development of PEC biosensors.

In Situ Transmission Electron Microscopy Investigation on Fatigue Behavior of Single ZnO Wires under High-Cycle Strain

The fatigue behavior of ZnO nanowires (NWs) and microwires was systematically investigated with in situ transmission electron microscopy electromechanical resonance method. The elastic modulus and mechanical quality factors of ZnO wires were obtained. No damage or failure was found in the intact ZnO wires after resonance for about 10(8)-10(9) cycles, while the damaged ZnO NW under electron beam (e-beam) irradiation fractured after resonance for seconds. The research results will provide a useful guide for designing, fabricating, and optimizing electromechanical nanodevices based on ZnO nanomaterials, as well as future applications.

A self-powered ultraviolet photodetector based on solution-processed p-NiO/n-ZnO nanorod array heterojunction

We report fabrication of an all inorganic, self-powered and rapid-response ultraviolet (UV) photodetector using solution-processed p-NiO/ZnO-nanorod array heterojunction. The device exhibited a fast binary-response with a rise time of 0.23 s and decay time of 0.21 s. A large responsivity of 0.44 mA W−1 was achieved for a 0.4 mW cm−2 UV light irradiation at a zero-bias voltage. The self-powered performance could be attributed to the proper built-in electric field between ZnO and NiO arising from the well-aligned energy-band structure of the device, which gives rise to a photovoltaic effect.